In various multistage turbomachines used for energy conversion, such as a gas turbine, a hot combustion gas expands through the turbine to produce rotational motion. Referring to FIG. 1, a gas turbine 10 is schematically shown. The turbine 10 includes a compressor 12, which draws in ambient air 14 and delivers compressed air 16 to a combustor 18. A fuel supply 20 delivers fuel 22 to the combustor 18 where it is combined with the compressed air 16 and the fuel 22 is burned to produce high temperature combustion gas 24. The combustion gas 24 is expanded through a turbine section 26, which includes a series of rows of stationary vanes and rotor blades. The combustion gas 24 causes the rotor blades to rotate to produce shaft horsepower for driving the compressor 12 and a load, such as an electrical generator 28. Expanded gas 30 is either exhausted to the atmosphere directly, or in a combined cycle plant, may be exhausted to atmosphere through a heat recovery steam generator.
The rotor blades are mounted to disks that are supported for rotation on a rotor shaft. Annular arms extend from opposed surfaces of adjoining disks to form pairs of annular arms each separated by a gap. A cooling air cavity is formed on an inner side of the annular arm pairs between the disks of mutually adjacent stages. In addition, a labyrinth seal may be provided on an inner circumferential surface of stationary vane structures that cooperate with the annular arms to form a gas seal between a path for the hot combustion gases and the cooling air cavity. Each annular arm includes a slot for receiving a sealing band, known as a “belly band”, which spans the gap between each annular arm pair to stop a flow of cooling air from the cooling air cavity into a path for the combustion gas 24. The sealing band may include multiple seal strip segments that extend in a circumferential direction. Each segment is configured to allow for thermal expansion during operation of the gas turbine. After reaching operating temperature, the segments become interconnected at lapped or stepped ends. FIG. 2 depicts an exemplary overlap arrangement 31 between adjacent first 33 and second 35 segments. The first 33 and second 35 segments include top 37 and bottom 39 overlap portions, respectively. The top 37 and bottom 39 overlap portions are each approximately one-half the thickness of the remaining portions of a segment 33, 35.
The sealing band is subjected to harsh environments including thermal cycling and high frequency vibrations that cause fretting wear in the overlap portions 37, 39. This leads to an undesirable loss of sealing capability due to leakage around worn areas of the overlap portions 37, 39. In addition, differential pressure and cooling flow may generate dynamic vibration and cause “hammering” or impact wear that can accelerate fretting wear. Such wear necessitates field replacement of the segments, thus increasing operating costs. Therefore, it is desirable to extend the wear life of the segments of a sealing band.